Geoffrey Arthur Prime, the British intelligence officer accused of spying for the Soviet Union for nine years, may have been only one member of a Soviet spy ring operating out of Britain's supersecret electronic listening post in Cheltenham 85 miles west of London, U.S. intelligence sources said yesterday.

"Prime is the tip," one source said, "perhaps not of an iceberg, but almost surely of something bigger than Prime himself."

Only Prime has been arrested and charged with espionage under Britain's 70-year-old Official Secrets Act, and there have been no public suggestions that anybody but the 44-year-old translator of Russian was spying for the Soviets.

But U.S. intelligence officials are seriously concerned that Prime was not acting alone on behalf of the Soviets at Cheltenham, the sources said.

One reason for suspicion that Prime was part of a ring is the wide scope of information said to have been leaked from Cheltenham to the Soviet Union, the sources said. Not only were codes to break secret Soviet messages leaked but also widespread information about deployment of North Atlantic Treaty Organization divisions throughout western Europe, the sources said.

U.S. intelligence sources believe that more than one person had to have access to such information at Cheltenham to have leaked it to the Soviets.

Another reason for suspecting that Prime did not act alone, the sources said, is the slow way in which British intelligence is said to have informed its U.S. counterparts of Prime's activities and his arrest in July on espionage charges, the sources said.

The sources said British intelligence knew two years ago that Prime was spying for the Soviets but took a year to tell the United States and another year to arrest him.

"Their excuse was that they were hoping Prime would lead them to other Soviet agents if there were others," one U.S. intelligence source said. "But nothing of what they have said explains why it took the British so long to describe to us what happened."

Whether Prime acted alone or with others, his arrest is sure to trigger new U.S. concern about British security at Cheltenham, where Prime worked from 1968 to 1977.

The huge radio antennas above ground and giant computers below ground there are mirror images of the antennas and computers used by the U.S. National Security Agency at Fort Meade to eavesdrop on radio and telephone traffic around the world.

So closely is Cheltenham tied with Fort Meade that they routinely exchange secrets, codes, ways to break codes and recorded computer tapes, sources said. Next year, according to a recently published book about the NSA called "The Puzzle Palace," the computers at Fort Meade and Cheltenham will be tied together by a secret cable system.

Cheltenham and Fort Meade exchange officers and even exchange eavesdropping duties annually in some countries to make sure that nothing is being missed by the two listening posts, the sources said.

"The two agencies are so close that they try to avoid duplication the way two agencies in the same government would avoid it," one source said. "For instance, the United States more or less lets the British listen in for us at Hong Kong, and the British more or less let us listen in for them on all of Latin America."

Key questions being asked in U.S. intelligence circles are how Prime managed to escape detection in nine years at Cheltenham and how he passed so much information to the Soviets, presuming he acted alone, the sources said.

Prime was first arrested on an unrelated charge of molesting children and was arraigned on espionage charges. He is expected to stand trial Nov. 19.

"The question is, why didn't the British know about Prime's proclivities before he was hired at Cheltenham in 1968?" said a psychiatrist who has worked for the Central Intelligence Agency.

What most concerns U.S. intelligence officials is what they regard as lax security at Cheltenham, the sources said. Clearance checks at Cheltenham are "not thorough enough," one U.S. intelligence official said.

Any of the estimated 6,000 persons who work at Cheltenham can carry out classified documents because they are not asked by guards to open their briefcases when they leave, the U.S. sources said.

Some U.S. intelligence officials cite Prime as the latest in a string of British intelligence experts who turned to Soviet espionage, starting with the Burgess-Maclean-Philby affair two decades ago. Others are more realistic, recalling U.S. intelligence officers who have dealt secrets to the Soviets.

Said one: "We didn't have documents checks at the CIA or the NSA until people were found to be walking out with documents they were giving to Russians. It's easy to forget your own mistakes."